1. Field of the Invention
The present invention relates to a light detector and more particularly to a converging lens to collect light emitted from different directions on a light detecting surface to reduce the overall size of the light detector.
2. Discussion of the Related Art
A light detector for use as a photo diode, or the like, generally needs to have a large converging lens to efficiently convert from light to electric power. FIG. 3(a) is a cross-sectional view along a longitudinal axis Z of a conventional light detector 90 having a lens 3 formed by resin molding. FIG. 3(b) is a cross-sectional view along an axis Z in a focusing direction of another conventional light detector 90' whose envelope is a combination of a cylindrical case 4 having an aperture on one end, and a converging lens 5 covering the aperture.
The light detector 90 in FIG. 3(a) comprises a photo sensing chip 1 having a light detecting surface 1', at least one electrode 2 connected to the photo sensing chip 1, and a lens 3 having a spherically or non-spherically curved end 7. In this composition, directivity is determined by a distance L from the light detecting surface 1' of the photo sensing chip 1 to the curved end 7 of the lens 3 and a radius of curvature of the curved end 7. A larger lens 3 is used to obtain larger light detection output while keeping the directivity.
The conventional light detector 90' in FIG. 3(b) comprises a photo sensing chip 1 having a light detecting surface 1', at least one electrode 2 connected to the photo sensing chip 1, a cylindrical case 4 having an aperture on one end, and a converging lens 5 covering the aperture. In this composition, the length L' from the light detecting surface 1' of the photo sensing chip 1 to the top portion 5a on the convex surface of the converging lens 5 is smaller than the length L of FIG. 3(a) to reduce the overall size of the light detector 90'.
The conventional light detectors 90 and 90' each have several problems. As shown in FIG. 4, it is difficult to obtain sufficient directivity onto the photo sensing chip 1 and light incident to the lens 3 when the height h from the substrate 6 to the curved end 7 of the lens 3 is limited.
The light detector composition 90 in FIG. 3(a) minimizes the amount of undetected incident light rays because the lens 3 is a single unit instead of a combination of a lens and a case. However, since the directivity is determined by both the distance L from the light detecting surface 1' of the photo sensing chip 1 to the curved end 7 of the lens 3 and the radius of curvature of the curved end 7 of the lens, a diameter .o slashed. of the lens 3 has to be enlarged to obtain a sufficient amount of incident light while maintaining sufficient directivity. Accordingly, the height h also must be enlarged.
As for the light detector 90' as shown in FIG. 3(b), the transmitting efficiency of the incident light through the lens 5 is low because air exists between the light detecting surface 1' of a photo sensing chip I and the converging lens 5. Further, the composition of the light detector 90' does not allow for the reflowing mounting method.